Collapsible sponge mattress



FIG. 1 is a top view (open position) of a collapsible sponge mattress showing my design;

FIG. 2 is a bottom view (open position) thereof;

FIG. 3 is an isometric view (closed position) thereof;

FIG. 4 is an isometric view (closed position) thereof;

FIG. 5 is a top view (closed position) thereof;

FIG. 6 is a bottom view (closed position) thereof;

FIG. 7 is a side view (closed position) thereof; and,

FIG. 8 is a side view (closed position) thereof. 

The ornamental design for the collapsible sponge mattress, as shown and described. 